|"Ariel, girl, there is no 'reason' when it comes to chaos metal!" Rainbow's voice cracked. "There's just... just... I mean look at this!" She gestured wildly at the floating mess. "It's nothing but diarrhea and death!"
"Death diarrhea! On a cosmic level!"
|- Ofolrodi, "There's Always Worse Evil"|
Chaos Metal is a silvery material believed to be formed out of Discord's bone. It most often appears in the form of "chaos strips"; small bits of the metal which are typically used to summon chaos monsters. Examples of this include the Xonan warriors of the Sacred Hold, and Sladesteed in Windthrow. It appears to be a naturally forming material, as it is most frequently found near places that have open mines and (coincidentally?) access to the Machine World. The presence of chaos metal in the earth is usually indicated by an unnatural haze or fog in the surrounding landscape.
Astral explains: “They're leftover relics from the Chaos Wars, when Discord ravaged the world...They were used to summon abominations that Discord had crafted in the nether. Rumor is that it's made out of his special, regenerative bone. It emulates how the great Lord of Chaos was capable of creating matter out of seemingly-nothing. He was merely reaching into an alternate dimension of discordant energies. The chaos strips function in the same way, but each one of them is enscribed with the ability to only summon one thing.”
A sarcophagus composed of chaos metal was used to hold Rainbow Dash in stasis during Belle's sequencing in the early chapter of Eljunbyro. Plans were uncovered for a similar chamber for transporting Rainbow to the battlefield as part of Ledomare's strategy for weaponizing her. Somehow, the metal is uniquely able to contain Rainbow's chaos form. How Ledomare's scientists knew this, or where they obtained the metal from is not known (verify).